Up until now, if you didn't want a specific patient to receive appointment confirmation e-mails, you had to remove their e-mail address from Cliniko. This was inconvenient because it also prevented other messages (such as invoices) from being sent to that patient.
Now when you edit a patient's details, you will see a new setting under Communication Preferences:
The new "Send appointment confirmation e-mails" setting is enabled in all patients by default, so if you want your account to behave as it always did you don't need to do anything to it. Cliniko still respects the account-wide settings for confirmation e-mails, too, so if they're disabled there no patients will receive them even when the checkbox above is marked for them.